Drewes, MarcoGeoris, YannisYannisGeoris2025-05-142025-05-142025-05-142021https://hdl.handle.net/2078.2/24464Heavy neutrinos are new hypothetical particles that can solve two of the greatest mysteries of modern physics. They can explain the origin of the non-zero neutrino masses through the type-I seesaw mechanism and can explain the origin of baryonic matter through leptogenesis. These new particles are currently searched for at a various range of high-energy experiments (NA62, CMS, Atlas, T2K). These searches will even be strengthened in the next few years by upcoming experiments such as DUNE, SHiP or MAHUSLA. There is therefore a need in the particle physics community for predictions for the masses and couplings to Standard Model particles of these heavy neutrinos. While early models of leptogenesis needed large masses, untestable at present-day experiments, the last two decades have seen an increased interest in so-called low-scale leptogenesis models feasible for masses even way below the electroweak scale, therefore testable at diverse current and near-future experiments. In the present thesis, we investigated the case where three generations of heavy neutrinos participate to leptogenesis and account for neutrino masses. We for the first time mapped the range of couplings to the Standard Model neutrinos for which leptogenesis is a viable solution and this for heavy neutrino masses ranging from 50 MeV to 70 TeV, thereby covering the entire range currently accessible to experiments. We limited ourselves to an approximately mass degenerate scenario, where the largest couplings are expected to appear. We showed that the range for allowed coupling strength of the heavy neutrinos is way larger than in the scenario with only two heavy neutrinos. The most optimistic cases would then lead to the detection of, for instance, thousands of displaced vertices at HL-LHC, a number sufficient to allow experimentalists not only to discover these heavy neutrinos, but also to constrain their properties (branching ratio of the decays, proportion of lepton number violating processes,...).Right-handed neutrinosCosmologyType-I seesawBSM physicsLow-scale leptogenesistext::thesis::master thesisthesis:33003